This application is claims foreign priority based upon Japanese Patent Applications No. 2001-76959 filed on Mar. 16, 2001, and No. 2002-10324 filed on Jan. 18, 2002, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a centrifugal blower including a centrifugal multi-blade fan having plural blades arranged around a rotation axis. More particularly, the present invention relates to a noise-reduction structure for reducing noise caused in the centrifugal blower. The present invention is suitably used for a blower of a vehicle air conditioner.
2. Description of Related Art
In a conventional centrifugal blower described in JP-U-50-82706 or in JP-U-54-97805, a nose cap at a side of a suction port is made smaller than a nose cap at a side opposite to the suction port, so that a NZ noise is reduced while it can prevent an air-blowing amount from being reduced and a specific noise from being increased. Here, the NZ noise is a noise caused when air blown from a centrifugal multi-blade fan collides with a nose portion of a scroll casing. However, in this case, because the nose cap at the side of the suction port is made smaller than the nose cap at the opposite side of the suction port, a radial dimension of the scroll casing on the opposite side of the suction port needs to be increased for enlarging a passage-section area.
In addition, when a dimension (i.e., scroll radius) between a rotation axis of the centrifugal multi-blade fan and the scroll casing is simply set to become larger from a scroll start portion toward a scroll finish portion of the scroll casing, a low-frequency noise may be caused.
In view of the foregoing problems, it is an object of the present invention to provide a centrifugal blower which reduces low-frequency noise while specific noise is reduced.
According to the present invention, in a centrifugal blower, a centrifugal fan is disposed in a scroll casing to have a space between the centrifugal fan and the scroll casing at a nose portion, through which a scroll start side and a scroll finish side communicate with each other in the scroll case. The scroll case has an end in the vicinity of the nose portion, at a reverse side with a rotation direction of the centrifugal fan. In addition, the end is tilted relative to a direction parallel to the rotation axis, toward the rotation direction, from a side of the suction port to a side opposite to the suction port. Accordingly, a re-circulation air flow from an air outlet side (scroll finish side) into the space between the outer periphery of the centrifugal fan and the inner wall of the scroll case in the nose portion, can be introduced toward a downstream air-blowing side of the centrifugal fan with the air blown by the centrifugal fan, without being reversely introduced between blades of the centrifugal fan. Thus, it can restrict an interference between the re-circulation flowing air and the sucked air, and thereby reducing the low-frequency noise.
Alternatively, in the present invention, the scroll case has a first wall part on the side of the suction port, and a second wall part on the side opposite to the suction port, in the vicinity of the nose portion. In addition, the first wall part is disposed to protrude from the second wall part toward a reverse side with the rotation direction. Even in this case, the same advantage described above can be obtained.
Preferably, in a predetermined range from the nose portion in the rotation direction, a first clearance dimension between an outer periphery of the centrifugal fan and an inner wall of the scroll casing on the side of the suction port, is smaller than a second clearance dimension between the outer periphery of the centrifugal fan and the inner wall of the scroll casing on the side opposite to the suction port. In this case, the NZ noise and the specific noise can be further reduced while the low-frequency noise can be reduced.
Preferably, a scroll angle of the scroll casing is continuously changed in such a manner that the first clearance dimension is equal to the second clearance dimension in a range of the scroll angle between 20 degrees and 135 degrees. Therefore, noise generated in the blower can be effectively reduced. Further, in the nose portion, a ratio of the second clearance dimension to an outer diameter of the centrifugal fan is in a range of 0.1-0.16. In this case, the low-frequency noise, the NZ noise and the specific noise can be readily reduced.